There are many different ways to craft a terrain and the choice of a given method is entirely subjected to the requirements of a project and its targeted visual output. Should the visual requirement of a terrain is meant for cinematic playback (e.g. 4K Resolution), then the terrain would need the highest level of details that a production pipeline could provide. To create such highly detailed terrain, the workflow is going to be very complex as the process to replicate a nature environment that can stand for close-up shots is tough!